The present invention relates to a method of improving the electrical conductivity of a shaped resin article and an electrostatic coating process.
A known method of applying electrostatic coating after improving the electrical conductivity of a shaped resin article includes, for example, a method of forming an electrically conductive primer layer by coating an electrically conductive paint containing an electrically conductive metal powder on the surface of a shaped resin article to provide electrical conductivity and then applying electrostatic coating as disclosed in JP-A-50066538 or a method of kneading an electrically conductive inorganic substance such as carbon black, carbon fiber or electrically conductive mica into a resin molding material, then molding the same and applying electrostatic coating thereto.
However, when an electrically conductive primer layer is formed on the surface of a shaped resin article as disclosed in JP-A-50066538, adhesion between the surface of the resin article and the electrically conductive primer is poor and a plurality kinds of electrically conductive primer layers have to be formed as a plurality of layers in order to improve the drawback. This not only brings about a problem in view of the electrical conductivity and the productivity but also leads to a problem in view of coating losses or increased costs by the use of a plurality kinds of electrically conductive primers.
Furthermore, when electrostatic coating is applied to a shaped article kneaded with an electrically conductive inorganic substance such as carbon black, carbon fiber, conductive mica or the like, since the electrically conductive substance must be kneaded in a large amount into the resin molding material, this results in problems of tending to detract from the physical properties of the resin article and affects the color on the electrostatically coated surface by the coloration of the resin article.
Recently, there is disclosed a method as in JP-A-03101875 of kneading a complex of a polyoxyalkylene polyol with a soluble electrolyte salt into a resin molding material, molding the kneaded mixture, subjecting the surface of the resultant shaped article to a plasma treatment and then applying electrostatic coating. However, the method is poor in the productivity since the plasma treatment is a batch operation and involves a problem that the article has to be treated under a reduced pressure.